1. Field of the Invention
The present invention relates generally to a method for creating, updating, and recording seamless presentation information of moving picture data in a rewritable recording medium, and more particularly, but not by way of limitation, to a method for creating seamless presentation information with no unnecessary information fields and for effectively updating seamless presentation information when some video objects are erased.
2. Description of the Related Art
Optical disks have come into wide use since the advent of compact disc (CD) and the demand for optical disks is expected to grow steadily with popularization of digital versatile disk (DVD). Optical disks include read-only disks such as CD-ROM and DVD-ROM, write-once disks such as CD-R and DVD-R, and rewritable disks such as CD-RW and DVD-RAM. The specification of DVD-RTRW, which is standard writing/reading format of a rewritable disc, has not released yet and standardization for the DVD-RTRW is under way.
As rewritable optical disks like DVD-RAM are of immensely large capacity, users may store a variety of data such as moving pictures, still pictures, audio data, and the like on a single recording medium. Each time a new data file is recorded on a rewritable recording medium, navigation information for locating the data file after recording is created and recorded along with the data file on the recording medium. The recorded navigation information is referred to whenever the relevant data file is accessed.
Navigation information regarding all data files stored on a recording medium is contained in a navigation data table as shown in FIG. 1, which is recorded as a single navigation data file on the recording medium. Accessing the recording medium entails loading the navigation data file into a memory, wherein the navigation data reside all the time. When recording a moving or still picture on the recording medium, the area in which the picture file will be recorded is determined with reference to the navigation information. Recording a picture file always accompanies creating management information regarding the recorded picture file and updating the navigation data file to include the newly created management information.
Management data pertaining to moving pictures comprise movie video object information (M_VOBI) and movie video object presentation order information (Cell Information or simply CI). Suppose that a moving picture file is composed of n movie video objects (M_VOBs) M_VOB#1˜M_VOB#n as shown in FIG. 2. Then, n M_VOBIs (M_VOBI#1˜M_VOBI#n in FIG. 2) and n CIs (CI#1, CI#2, CI#4, shaded in FIG. 2) corresponding to the n M_VOBs are created in the same order that the n M_VOBs are recorded. The created M_VOBIs and CIs are stored in the movie A/V file information table (M_AVFIT) and the original program chain information table (ORG_PGCIT) of the navigation data shown in FIG. 1, respectively.
When the recording medium is accessed, the navigation data file is read from the recording medium and loaded into a memory as mentioned before. If reproduction of a moving picture is requested, M_VOBIs and CIs relevant to the requested moving picture file are read from the M_AVFIT and ORG_PGCIT of the navigation data table, respectively. In reference to the obtained M_VOBIs and CIs, the requested moving picture file can be located from the recording medium and reproduced.
As shown in FIG. 1, the movie A/V file information table (M_AVFIT) comprises movie A/V file information table information (M_AVFITI) wherein information on the M_AVFIT such as the end address of the M_AVFIT is stored and movie A/V file information (M_AVFI#1). The M_AVFI#1 further comprises movie A/V file general information (M_AVFGI) wherein general information on the M_AVFI such as the number of M_VOBIs contained in the M_AVFI is stored and M_VOBIs, M_VOBI#1˜M_VOBI#n. Each of M_VOBIs comprises movie VOBI general information (M_VOBIGI) wherein the ID code of the relevant VOB is stored, movie VOB stream information (M_VOB_STI) wherein video and audio attributes of the relevant VOB is stored, seamless presentation information (SMLI) wherein information for seamless presentation of successive MOVs (M_VOB#i and M_VOB#i+1, i=1˜n) is stored, and time map information (TMAPI) wherein information for special playback or time search is stored.
A moving or still picture file is recorded on the recording medium as a group of video objects (VOBs). For reproducing moving picture data received and recorded as successive data stream, it is necessary to present the relevant VOBs seamlessly. On the other hand, seamless presentation is not always necessary for moving picture data obtained through repeated recording-stop process. If successively inputted picture data contain still pictures as well as moving pictures, the picture data are recorded being classified into movie VOBs (M_VOBs) and still picture VOBs (S_VOBs). In this case, seamless presentation between the group of M_VOBs and the group of S_VOBs is not necessary, either.
When recording received picture data on the recording medium, it is therefore necessary to create information on whether to present successive VOBs forming the picture data seamlessly so that the information can be used in the course of data reproduction. Such information is recorded in the SMLI of the navigation data table shown in FIG. 1.
As shown in FIG. 1, the SMLI comprises a seamless presentation flag (SML_FLG) which indicates how to present the relevant VOB after the preceding VOB is presented (for example 1 indicates seamless presentation is needed, while 0 indicates seamless presentation is not necessary), the presentation start time of the first video field of the relevant VOB (VOB_V_S_PTM), the presentation end time of the last video field of the relevant VOB (VOB_V_E_PTM), system clock reference (SCR) of the first pack of the relevant VOB (VOB_FIRST_SCR), system clock reference of the last pack of the preceding VOB (VOB_LAST_SCR), VOB audio stop time (VOB_A_STP_PTM) which denotes pause time of audio at discontinuity in RTRW's PTM describing format between the current VOB and the preceding VOB, and VOB audio gap length (VOB_A_GAP_LEN) which denotes the discontinuity period at discontinued point between the current VOB and the preceding VOB.
As depicted in FIG. 3, a M_VOB is composed of a plurality of video object units (M_VOBUs), each of which comprises a plurality of video packs (V_PAKs), subpicture packs (SP_PAKs), and audio packs (A_PACKs).
The V_PAKs of each M_VOB are coded by MPEG-2 video encoding method. The first V_PAK comprises a pack header, a system header, a packet header, and video data as shown in FIG. 4A, while each of the other V_PAKs comprise a pack header, a packet header, and video data as shown in FIG. 4B. The system clock reference (SCR) and presentation time stamp (PTS) needed for presentation of the video pack are recorded in the pack header and packet header, respectively.
The A_PAKs of each M_VOB are coded by one of the following encoding methods: linear PCM coding as shown in FIG. 5A, Dolby AC-3 coding as shown in FIG. 5B, and MPEG-2 audio coding as shown in FIG. 5C. Without regard to the adopted encoding method, the SCR and PTS are recorded in the pack header and packet header, respectively.
A M_VOB comprises multiple top fields (or even fields) and bottom fields (or odd fields) as shown in FIG. 6, and a pair of top and bottom fields forms a frame. The PTS of the first field of the M_VOB amounts to the presentation start time of the VOB (VOB_V_S_PTM) and the sum of the PTS of the last field and 1/60 sec amounts to the presentation end time of the VOB (VOB_V_E_PTM).
As mentioned earlier, seamless presentation of audio and video data may not be necessary provided the moving picture is taken through repeated record-stop process or the picture data contain both moving and still picture data. In such cases, therefore, the fields of VOB_FIRST_SCR and VOB_LAST_SCR in the SMLI are unnecessary since such fields are utilized only for seamless presentation of successive VOBs.
In conventional navigation data structures, whether the fields may be necessary or not, every SMLI contains the fields of VOB_FIRST_SCR and VOB_LAST_SCR, which unnecessarily increases the amount of navigation data. Moreover, when some VOBs are erased from picture data, the SMLI of the VOB following the removed VOB should be appropriately dealt with, which has not been sufficiently considered.